Re: [PATCH v2] pci: ensure valid link status bits for downstream ports

[Alex Williamson <alex.williamson@redhat.com>]

On Tue,  3 Dec 2024 13:19:28 +0100
Sebastian Ott <sebott@redhat.com> wrote:

> PCI hotplug for downstream endpoints on arm fails because Linux'
> PCIe hotplug driver doesn't like the QEMU provided LNKSTA:
> 
>   pcieport 0000:08:01.0: pciehp: Slot(2): Card present
>   pcieport 0000:08:01.0: pciehp: Slot(2): Link Up
>   pcieport 0000:08:01.0: pciehp: Slot(2): Cannot train link: status 0x2000
> 
> There's 2 cases where LNKSTA isn't setup properly:
> * the downstream device has no express capability
> * max link width of the bridge is 0
> 
> Move the sanity checks added via 88c869198aa63
> ("pci: Sanity test minimum downstream LNKSTA") outside of the
> branch to make sure downstream ports always have a valid LNKSTA.
> 
> Signed-off-by: Sebastian Ott <sebott@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  hw/pci/pcie.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>


> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 0b455c8654..1b12db6fa2 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -1113,18 +1113,22 @@ void pcie_sync_bridge_lnk(PCIDevice *bridge_dev)
>          if ((lnksta & PCI_EXP_LNKSTA_NLW) > (lnkcap & PCI_EXP_LNKCAP_MLW)) {
>              lnksta &= ~PCI_EXP_LNKSTA_NLW;
>              lnksta |= lnkcap & PCI_EXP_LNKCAP_MLW;
> -        } else if (!(lnksta & PCI_EXP_LNKSTA_NLW)) {
> -            lnksta |= QEMU_PCI_EXP_LNKSTA_NLW(QEMU_PCI_EXP_LNK_X1);
>          }
>  
>          if ((lnksta & PCI_EXP_LNKSTA_CLS) > (lnkcap & PCI_EXP_LNKCAP_SLS)) {
>              lnksta &= ~PCI_EXP_LNKSTA_CLS;
>              lnksta |= lnkcap & PCI_EXP_LNKCAP_SLS;
> -        } else if (!(lnksta & PCI_EXP_LNKSTA_CLS)) {
> -            lnksta |= QEMU_PCI_EXP_LNKSTA_CLS(QEMU_PCI_EXP_LNK_2_5GT);
>          }
>      }
>  
> +    if (!(lnksta & PCI_EXP_LNKSTA_NLW)) {
> +        lnksta |= QEMU_PCI_EXP_LNKSTA_NLW(QEMU_PCI_EXP_LNK_X1);
> +    }
> +
> +    if (!(lnksta & PCI_EXP_LNKSTA_CLS)) {
> +        lnksta |= QEMU_PCI_EXP_LNKSTA_CLS(QEMU_PCI_EXP_LNK_2_5GT);
> +    }
> +
>      pci_word_test_and_clear_mask(exp_cap + PCI_EXP_LNKSTA,
>                                   PCI_EXP_LNKSTA_CLS | PCI_EXP_LNKSTA_NLW);
>      pci_word_test_and_set_mask(exp_cap + PCI_EXP_LNKSTA, lnksta &